Add help text communicating that a TURN server is not usually required.

static/partials/settings.html

@@ -286,6 +286,7 @@
           <div ng-show="clientSideTurn">
               <legend>{{_('Turn')}}</legend>
               <div>
+                <p>{{_('Normally a TURN server is not required. Only use in cases when peer to peer connections are blocked by a firewall.')}}</p>
                 <div class="form-group">
                   <label class="col-xs-4 control-label">{{_('Turn urls')}}</label>
                   <div class="col-xs-8">